Air conditioners, heat pumps, dehumidifiers, and humidifiers, can collectively be called climate control systems. Air-conditioners, heat pumps, and dehumidifiers circulate air by a cooled surface. As the warm air is cooled below its dewpoint, water condenses and accumulates on the cooled surface and typically falls into a collection reservoir where eventually the collected water drains to the outdoors via a drain line. In the wet and cool condensate pan environment, conditions are favorable for the growth of microbes which can be entrained by the passing air. Depending on the operation or duty cycle of the particular system, this water sometimes remains stagnant for long time periods, thereby promoting microbial and fungal growths on water-contacted parts and surfaces.
During winter months, humidifiers are sometimes used to humidify dry air by passing the dry air across a moist surface. Systems such as pan humidifiers, portable humidifiers, power wetted-element humidifiers, atomizing humidifiers, ultrasonic humidifiers, and rigid media humidifiers are widely used. A humidifier by nature requires a water source which is evaporated into drier air. These water sources can promote microbial and fungal colony growths that could be entrained into the ventilation system via the passing air flow. Treating the water used in these systems with biocides can dramatically reduce the likelihood that airborne toxins are entrained.
The dispersion of microbes such as bacteria, virus, mold, and fungus can be the source of sickness to exposed occupants in the climate controlled area. For example, Legionella pneumophilia has been found to exist in such an environment and has been linked to Legionnaire's disease. Other microbes can contribute to "sick home" or "sick building" syndrome. Many people are also allergic to the molds and fungus entrained in the dwelling's ventilation as the air passes over contaminated water.
By treating the source where these microbes can be entrained by the climate control system's circulating air, these sometimes toxic airborne microbes can be much reduced or even eliminated. One way to eliminate these microbes is to treat the water contained in the water reservoir or source.
It is usually not a trivial matter to access a climate control system such as an air-conditioner air handling unit. Hence, for minimal maintenance, the treatment of the microbe-laden water in these sealed systems would best be accomplished by using an automatic time-released or long duration method. For example, one tablet or packet could reduce bacteria, fungi, algae and mold in a water reservoir for an entire summer or spring season (e.g., about 3 months or longer).
Metals such as silver (Ag), nickel (Ni), zinc (Zn), copper (Cu), and tin (Sn) are known in the art as effective biocides. For example, Ag is effective against virus and bacteria. In particular, a concentration of about 0.02 ppm (or 20 ppb) in water is effective against Legionella pneumophilia. Cu is also an effective algaecide and in some cases a bactericide. Other metals can also be effective against different microbes to differing degrees.
Metals such as these used as a biocide are typically provided in a water-soluble form. Hence, these materials are generally added to water systems as a water soluble salt. In order to extend the biocidal efficacy of these highly soluble salts over an extended period of time, the compounds must be metered into the water mechanically or added manually on a schedule. A better method of introducing these effective metals into the water would be a controlled dissolution. Such a controlled dissolution process would drastically reduce the manpower and equipment needed to provide the biocidal treatment.
Equally important in an aqueous biocidal metal application is the stability of those metal ions in solution. There are many anions present in water with the potential to precipitate out the metal ions, and since their availability in solution is necessary to be effective against the microbes, a way of retaining the metals in solution is highly beneficial. If provisions are not made to ensure some level of these ions in solution, they will precipitate out negating their effect against microbes, and additional materials will need to be added costing the user more in raw materials and maintenance. One known technique to ensure that these effective compounds remain in solution where they are effective against microbes is through the use of chelating agents which have a stronger affinity toward the metal ions than do the anions present in the water. Certain chelating agents such as salicylic acid (SA) are also generally known by those skilled in the art to be biocides. For example, SA is known to be an effective fungicide. Hence, the use of chelating agents such as SA along with the metal biocides will provide dissolved and stable chelated metal ions as well as a dissolved, metal free chelating agent that can also supplement the metal biocide.